Evaluation of Ti<Subscript>3</Subscript>Si Phase Stability from Heat-Treated,Rapidly Solidified Ti-Si Alloys

Ti-base alloys containing significant amounts of silicon have been considered for high temperature structural applications. Thus, information concerning phase stability on the Ti-Si system is fundamental and there are not many investigations covering the phase stability of the Ti₃Si phase, specially its dependence on oxygen/nitrogen contamination. In this work the stability of this phase has been evaluated through heat-treatment of rapidly solidified Ti-rich Ti-Si alloys at 700 °C and 1000 °C. The rapidly solidified splats presented nanometric scale microstructures which facilitated the attainment of equilibrium conditions. The destabilization of Ti₃Si due to oxygen/nitrogen contamination has been noted.     

Start up of biological sequencing batch reactor (SBR) and short‐term biomass acclimation for polyhydroxyalkanoates production

BACKGROUND: The adaptation/selection of mixed microbial cultures under feast/famine conditions is an essential step for polyhydroxyalkanoates (PHA) production. This study investigated the short‐term adaptation of a mixed microbial culture (activated sludge) during the start up of a sequencing batch reactor (SBR). RESULTS: Four different SBR runs were performed starting from different inocula and operated at the same organic load rate (8.5 gCOD L^?1 d^?1) and hydraulic retention time (1 day). At 3–7 days from SBR start up, the selected biomass was able to store PHA at comparable rate and yield with those obtained after long‐term acclimation. Independently from the time passed, a short feast phase was the key parameter to obtain PHA storage at high rate and yield in the following accumulation stage (244 mgCOD g^?1CODnonPolym h^?1 for specific storage rate and 48% COD COD^?1 as PHA content in the biomass). The DGGE profiles showed that the good storage performance and the structure of the microbial community were not fully correlated. CONCLUSIONS: The results suggest a new strategy for operating the PHA accumulation stage directly in the SBR, after very short biomass adaptation, instead of using two separate reactors for biomass enrichment and PHA accumulation, respectively. © 2012 Society of Chemical Industry     

Citations versus journal impact factor as proxy of quality: could the latter ever be preferable?

In recent years bibliometricians have paid increasing attention to research evaluation methodological problems, among these being the choice of the most appropriate indicators for evaluating quality of scientific publications, and thus for evaluating the work of single scientists, research groups and entire organizations. Much literature has been devoted to analyzing the robustness of various indicators, and many works warn against the risks of using easily available and relatively simple proxies, such as journal impact factor. The present work continues this line of research, examining whether it is valid that the use of the impact factor should always be avoided in favour of citations, or whether the use of impact factor could be acceptable, even preferable, in certain circumstances. The evaluation was conducted by observing all scientific publications in the hard sciences by Italian universities, for the period 2004–2007. Performance sensitivity analyses were conducted with changing indicators of quality and years of observation.     

CHEMICAL AND TOXICOLOGICAL CHARACTERIZATION OF AIRBORNE TOTAL SUSPENDED PARTICULATE (TSP) AND PM 10 ORGANIC EXTRACTS

The relationship between chemical composition of airborne particulates and the genotoxicity has been investigated in the atmosphere of Rome, Italy. For this purpose, both total suspended particulate (TSP) and the PM ₁₀ fractions were collected daily inside a green park located in downtown, grouped on a weekly basis and speciated for their burdens of polycyclic aromatic hydrocarbons (PAH) and nitro-PAH. Concurrently, the genotoxicity of the organic extracts was evaluated by the Comet assay (SCGE: single cell gel electrophoresis) on human peripheral blood mononuclear cells (PBMC). The results indicate that organic extracts were able to induce DNA damage and a cytotoxic effect on PBMC. The TSP fraction was more cytotoxic than PM ₁₀ while the genotoxicity of both fractions was comparable. The genotoxic potential of the different samples was highly correlated to the amount of total PAH (correlation coefficient = 0.87), carcinogenic PAH (correlation coefficient = 0.88), B(a)P (correlation coefficient = 0.87) and to a less extend to the concentration of 1-nitropyrene (correlation coefficient = 0.66). The seasonal modulation suggests that in Rome the air is more toxic during winter, however in the warm season oxidized species including nitro-PAHs (evolving from secondary pollution) seem to balance the decrease of PAH concentration rates.     

Exploring the feasibility of volatile desorption studies by means of a quartz crystal microbalance with an integrated micro-heater

In this work the ability to perform desorption studies by using a micro-thermogravimetric device is demonstrated. The instrument consists of an oscillating quartz crystal microbalance with an integrated micro-heater that might turn out to be extremely useful in the study of the desorption of volatile compounds from refractory materials. The experiment here discussed has been performed by studying the release of adsorbed water from clay.Clay has been principally chosen because it is a material known for its ability to desorb and subsequently re-adsorb water at low temperatures and it might be considered a test mineral for a large number of applications, from first guess analysis of agricultural soil to quick inspection of materials of planetological interest (e.g., asteroid regolith).Results show that the device can be in stable operative conditions at 100 °C with 0.5 W of power supplied, allowing to measure the amount of desorbed water. In particular, as expected, it has been possible to assess that the desorbed water amount depends upon the working temperature, being less than 3 wt.% at 70 °C and about 5 wt.% at 90 °C.     

The role of auxiliary photons in state discrimination with linear optical devices

The role of auxiliary photons in the problem of identifying a state secretly chosen from a given set of L-photon states is analysed. It is shown that auxiliary photons do not increase the ability to discriminate such states by means of a global measurement using only optical linear elements, conditional transformation and auxiliary photons.     

Barrier properties of organic–inorganic hybrid coatings based on polyvinyl alcohol with improved water resistance

A comprehensive study of the gas barrier properties of hybrid organic–inorganic coatings formed by polyvinyl alcohol (PVOH) and Si‐SiO₂, obtained via sol–gel technique, was carried out. It has been shown that the oxygen, nitrogen and carbon dioxide transfer rates of barrier polymers such as poly(ethylene terephthalate) and oriented polypropylene can be further reduced, by up to two orders of magnitude, with a thin coating (1–2 μm) of PVOH/Si‐SiO₂. More notably, it has been observed that the material maintains this feature even after a prolonged contact with water, which is a strong solvent for PVOH. Direct moisture sorption measurements show that silica lowers the water uptake of PVOH and inhibits sorption‐induced swelling and plasticization of the polymer. Correlations between the gas transport properties of the hybrid coatings and factors such as the silica content, the type of polymeric substrate, the nature of penetrant and the temperature have been found, providing guidelines for the selection and design of multilayer materials for packaging applications. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Finite element analysis of reticulated ceramics under compression

This paper shows how finite element analysis can be used to study the effect of the morphological features of reticulated ceramics on their mechanical properties under compression. Quantitative morphological data, obtained by X-ray computed tomography (XCT) for a commercially available Si–SiC foam produced by the replica method, have been linked to a set of computer generated cells in which one morphological parameter was varied at a time. The findings indicate how the modification of some morphological features, which depend on the careful selection of appropriate and specific processing parameters, would enable the production of ceramic foams possessing higher strength for a given total porosity value.